The vapor phase reaction with hydrogen fluoride has long been used for the fluorination of aliphatic compounds containing halogens other than fluorine particularly chlorine and bromine. Chromium (III) oxide catalysts have been used for reactions of this type. Chromium (III) oxides used for this reaction have been obtained by reduction of chromium (VI) oxide CrO.sub.3 with ethanol, by dehydration of the commercial pigment "Guignet's Green", and by precipitation of a water-containing chromium (III) trihydroxide by treating aqueous solutions of chromium (III) nitrate or other water-soluble salts with an alkaline reagent. Although chromium (III) oxides so obtained have long been considered to be amorphous, it has recently been found by a combination of X-ray and electron diffraction analysis that these oxides do have a crystal structure and that the chromium (III) oxides so prepared exhibit a .gamma.-CrOOH orthorhombic crystallinity.
While the fluorination processes previously known provided a satisfactory means of replacing halogens with fluorine a continuing need exists for processes which operate effectively with a reduced need for catalyst replacement.